Bonding junction structure

ABSTRACT

Provided is a bonding joining structure in which a heat generating body and a support including a metal are joined to each other via a joint portion composed of a sintered body of copper powder. The support contains copper or gold, the copper or gold being present in at least an outermost surface of the support. An interdiffusion portion in which copper or gold contained in the support and copper contained in the sintered body is formed so as to straddle a bonding interface between the support and the sintered body. Preferably, a copper crystal structure having the same crystal orientation is formed in the interdiffusion portion so as to straddle the bonding interface.

TECHNICAL FIELD

The present invention relates to a bonding joining structure, and moreparticularly relates to a bonding joining structure that is preferablyused as a die bonding joining structure between a die of a semiconductordevice and a metal support.

BACKGROUND ART

With regard to bonding of a semiconductor device, Patent Document 1discloses a semiconductor apparatus having: a semiconductor device thathas a collector electrode on one surface and an emitter electrode on theother surface; and an insulating substrate that has a first electrodeinterconnect on one surface. The first electrode interconnect of theinsulating substrate and the collector electrode of the semiconductordevice are connected to each other via a first bonding layer. This firstbonding layer is a sintered layer obtained by sintering a bondingmaterial and a reducing agent. The bonding material contains a metalparticle precursor that is composed of silver carbonate and the like.The reducing agent is composed of particles of metal carboxylate thathave a melting temperature of 200 degrees or more. The semiconductordevice and the sintered layer are directly joined to each other as aresult of metallic bonding. The technique disclosed in this document isaimed at enabling bonding through metallic bonding at a bondinginterface to be realized at a lower temperature.

CITATION LIST

Patent Document

-   Patent Document 1: JP 2012-094873A

SUMMARY OF INVENTION

Incidentally, reducing power loss in inverters and converters is anessential issue in many fields such as automobiles, household electricalappliances, and industrial equipment. To address this issue, varioussemiconductor devices using new materials such as SiC and GaN in orderto significantly improve the energy utilization efficiency of equipmenthave been proposed. These semiconductor devices involve the generationof a large amount of heat during operation. For this reason,semiconductor packages need to be provided with sufficientcountermeasures for heat dissipation so as to prevent damage to thesemiconductor devices caused by generated heat. Generally, a lead frameor a substrate to which a semiconductor device is joined and fixed isused for heat dissipation. Although the technique disclosed in PatentDocument 1 above relates to bonding of a semiconductor device, thistechnique focuses on the bonding temperature and does not giveconsideration to heat dissipation.

Therefore, it is an object of the present invention to improve a bondingstructure for various heat generating bodies including a die of asemiconductor device, and more particularly to provide a bondingstructure that can efficiently dissipate heat generated from a heatgenerating body.

The present invention provides a bonding joining structure in which aheat generating body and a support including a metal are joined to eachother via a joint portion composed of a sintered body of copper powder,

wherein the support contains copper or gold, the copper or gold beingpresent in at least an outermost surface of the support, and

an interdiffusion portion in which copper or gold contained in thesupport and copper contained in the sintered body are diffused to eachother is formed so as to straddle a bonding interface between thesupport and the sintered body.

The present invention especially provides the bonding joining structure,wherein the bonding joining structure is a die bonding joining structurein which a die of a semiconductor device, the die serving as the heatgenerating body, and the support including a metal are joined to eachother via the joint portion composed of the sintered body of the copperpowder,

the support contains copper or gold, the copper or gold being present inat least the outermost surface of the support, and

the interdiffusion portion in which copper or gold contained in thesupport and copper contained in the sintered body are diffused to eachother is formed so as to straddle the bonding interface between thesupport and the sintered body.

The present invention also provides a bonding joining structure in whicha heat generating body and a metal support are joined to each other viaa joint portion composed of a sintered body of nickel powder,

wherein the support contains nickel, the nickel being present in atleast an outermost surface of the support, and

an interdiffusion portion in which nickel contained in the support andnickel contained in the sintered body are diffused to each other isformed so as to straddle a bonding interface between the support and thesintered body.

The present invention also provides a bonding joining structure in whicha heat generating body and a support including a metal are joined toeach other via a joint portion composed of a sintered body of silverpowder,

wherein the support contains silver, the silver being present in atleast an outermost surface of the support, and

an interdiffusion portion in which silver contained in the support andsilver contained in the sintered body are diffused to each other isformed so as to straddle a bonding interface between the support and thesintered body.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic vertical cross-sectional view showing a diebonding joining structure, which is an embodiment of a bonding joiningstructure of the present invention.

FIG. 2 schematically shows a relevant portion in FIG. 1 in an enlargedmanner.

FIG. 3 is a schematic vertical cross-sectional view (corresponding toFIG. 1) showing a die bonding joining structure, which is anotherembodiment of the bonding joining structure of the present invention.

FIG. 4(a) is a transmission electron microscope image of a portion inthe vicinity of a bonding interface of a die bonding joining structureobtained in Example 1, FIG. 4(b) is a magnified image of aninterdiffusion portion in FIG. 4(a), and FIG. 4(c) is a furthermagnified image of the image shown in FIG. 4(b).

FIG. 5 is a graph showing an element distribution in the vicinity of thebonding interface of a die bonding joining structure obtained in Example2.

FIG. 6 schematically shows an apparatus for evaluating heat dissipationproperties of die bonding joining structures obtained in examples andcomparative examples.

FIG. 7 shows transmission electron microscope images of a portion in thevicinity of the bonding interface of a die bonding joining structureobtained in Example 3.

FIG. 8 shows transmission electron microscope images of a portion in thevicinity of the bonding interface of a die bonding joining structureobtained in Example 4.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described based on preferredembodiments thereof with reference to the drawings. A bonding joiningstructure (hereinafter also referred to simply as “bonding structure”)of the present invention has a structure in which a heat generating bodyand a support including a metal are joined to each other via a jointportion. The joint portion is composed of a sintered body made of copperpowder. The type of heat generating body is not limited, and any memberthat generates heat during use can be considered as a heat generatingbody regardless of whether or not the member is intended for heatgeneration itself. A typical example of such a member is a die of asemiconductor device (hereinafter also referred to simply as “die”);however, the present invention is not limited to this, and, for example,a CPU, an LED device, a resistor, an electric circuit, and the like mayalso be used as the heat generating body. Moreover, in the presentinvention, another member that receives heat from a heat generatingbody, that is, a member that is joined to a heat generating body, forexample, and that is heated as a result of that member conducting theheat generated from the heat generating body is also considered as aform of heat generating body. Hereinafter, the present invention will bedescribed taking a die bonding joining structure in which a die is usedas the heat generating body as an example.

Dies are obtained by individually separating a plurality ofsemiconductor devices formed on a wafer, and are also called chips, baredies, and the like. A die is, for example, constituted by asemiconductor device such as a diode, a bipolar transistor, an insulatedgate bipolar transistor (IGBT), a field-effect transistor (FET), a metaloxide semiconductor field-effect transistor (MOSFET), or a thyristor.Examples of the constituent material for these semiconductor devicesinclude silicon (Si), silicon carbide (SiC), gallium nitride (GaN), andthe like. As will be described later, the bonding structure of thepresent invention has excellent heat dissipation properties, so thatwhen a semiconductor device that generates a large amount of heat, whichis a so-called power device, is used as a joining-target die of thepresent invention, the effects of the present invention are notablyachieved. Examples of such a power device include IGBTs, power MOSFETs,and various types of semiconductor devices composed of SiC and GaN.

The support is used to fix and support the die of the semiconductordevice. To this end, for example, a lead frame, a substrate, or the likeis used as the support. No matter what form the support takes, thesupport is made of metal. Since metals are materials having favorablethermal conductivity compared with other materials such as ceramics, useof a support made of a metal has the advantage of allowing heat that hasbeen generated during operation of the semiconductor device to be easilyreleased through the support.

There is no limitation on the type of the metal that composes thesupport, and the same materials as materials that have conventionallybeen used in the technical field of semiconductors can be used. Forexample, simple metals such as copper and aluminum can be used. Also,alloys such as a copper-iron alloy, an iron-nickel alloy, and astainless steel alloy can be used. Furthermore, a support having alaminated structure in which a plurality of layers of different metalmaterials are laminated in a thickness direction can also be used. Eachlayer may be composed of a simple metal or may be composed of an alloy.An example of the support having a laminated structure is a supporthaving a structure in which a base material layer is composed of asimple metal such as nickel, copper, or aluminum or an alloy and anoutermost layer is composed of gold alone. The support is in a state inwhich copper or gold is present in at least the outermost surface of thesupport. “Outermost surface” of the support refers to a surface of thesupport to which the heat generating body or the die of thesemiconductor device is fixed via a joint portion, that is, a surface ofthe support that opposes the joint portion. Examples of the support withcopper or gold being present in at least the outermost surface of thesupport include a support composed of copper alone, a support composedof a copper-based alloy such as a copper-gold alloy, a support having alaminated structure in which the base material layer is composed of asimple metal such as nickel, copper, or aluminum or an alloy and theoutermost layer is composed of gold alone, a support having a laminatedstructure in which the base material layer is composed of a simple metalsuch as nickel, copper, or aluminum or an alloy and the outermost layeris composed of an alloy that contains gold.

The die of the semiconductor device and the support are joined to eachother via the joint portion. The joint portion is composed of a sinteredbody of copper powder (hereinafter also referred to simply as “sinteredbody”). The joint portion can be formed over the entire region of anopposing surface of the die that opposes the support or in a portion ofthat opposing surface. The sintered body of copper powder that composesthe joint portion is formed by heating the copper powder containing aplurality of copper particles in a predetermined atmosphere at atemperature around the melting point of copper for a predeterminedperiod of time and bonding the copper particles such that a neckingportion is generated between the copper particles. The copper powder,which serves as the raw material for the joint portion, may be a powderof copper alone or may be a powder of a copper-based alloy that containscopper as the base material. Preferably, a powder consisting of copperalone is used. The sintered body of copper powder that composes thejoint portion may also contain other materials in addition to copper ora copper alloy, if necessary. Examples of such materials include organiccompounds that are used in order to prevent oxidation of the sinteredbody.

In the bonding structure of the present invention, an interdiffusionportion in which a metallic element contained in the support and aconstituent element contained in the sintered body are diffused to eachother is formed so as to straddle the bonding interface between thesupport and the sintered body. That is to say, a portion in which copperor gold contained in the support and copper contained in the sinteredbody are interdiffused is formed extending from the support side to thesintered body side across the bonding interface. This state will bedescribed with reference to FIG. 1. As shown in FIG. 1, a bondingstructure 1 has a structure in which a die 10 and a support 20 arejoined to each other via a joint portion 30 that is composed of asintered body 32 of copper powder containing a plurality of copperparticles 31. Furthermore, the die bonding joining structure 1 has abonding interface 40 between the support 20 and the sintered body 32. Inthe bonding structure 1, interdiffusion portions 41 in which themetallic element contained in the support 20 and the constituent elementcontained in the sintered body 32 are diffused to each other is formedso as to straddle the bonding interface 40. When the bonding structure 1is viewed along a vertical cross-sectional direction X, which is adirection along a cross section that is orthogonal to the bondinginterface, that is, when viewed along the up-down direction of the paperplane in FIG. 1, the interdiffusion portion 41 extends along thevertical cross-sectional direction X so as to straddle the bondinginterface 40. When viewed in that vertical cross section, with respectto a plane direction Y, which is a direction along the bondinginterface, that is, with respect to the left-right direction of thepaper plane in FIG. 1, at the bonding interface, the copper particles 31constituting the interdiffusion portions 41 each extend over a maximumregion R along the plane direction Y, on the support 20.

More specifically, as shown in FIG. 2, in the interdiffusion portions41, a plurality of primary particles 31 a constituting copper particles31 that are joined to the support 20 when viewed along the verticalcross-sectional direction X do not have grain boundaries along a planecorresponding to the bonding interface 40. A “primary particle” refersto an object that is recognized as the minimum unit of a particlejudging from the external geometric form of that object.

In the interdiffusion portions 41, constituent elements are bonded as aresult of metallic bonding. Specifically, in the case where the metallicelement that is present in the outermost layer of the support 20 is thesame as the constituent element of the sintered body 32, a single phasecomposed of a simple metal or an alloy is formed in the interdiffusionportions 41. In the case where the metallic element of the support 20 isdifferent from the constituent element of the sintered body 32, an alloyphase containing the metallic element of the support 20 and theconstituent element of the sintered body 32 is formed. “Metallicbonding” refers to bonding between metal atoms via free electrons.

Due to the fact that the configuration in which the interdiffusionportions 41 are formed in the bonding structure 1 and that theinterdiffusion portions 41 contain a phase in which constituent elementsare bonded through metallic bonding, free electrons are present in theinterdiffusion portions 41, and thus, the interdiffusion portions 41have favorable thermal conductivity. As a result, when the die 10 of thesemiconductor device generates heat due to operating, the generated heatis easily transferred to the support 20, which is a member that islocated on the opposite side to the die 10 across the joint portion 30.In other words, heat that has been generated from the die 10 of thesemiconductor device is dissipated. Thus, the semiconductor device isunlikely to be thermally damaged. This is important in terms of theoperational stability and the reliability of the semiconductor device.

In the case where the outermost surface of the support 20 is composed ofcopper alone and where the copper powder is also composed of copperalone, the interdiffusion portions 41 each contain a single phaseconstituted by a crystal structure consisting of copper alone. It ispreferable that, as shown in FIG. 2, in the crystal structure of thissingle phase, a portion 41 a that is located on the sintered body 32side of the bonding interface 40 and a portion 41 b that is located onthe support 20 side of the bonding interface 40 have the same crystalorientation. When the interdiffusion portion 41 a that is located on thesintered body 32 side of the bonding interface 40 and the interdiffusionportion 41 b that is located on the support 20 side of the bondinginterface 40 have the same crystal orientation as described above, thecrystal orientation intersects the bonding interface 40, free electronsmove smoothly between the interdiffusion portions 41 a and 41 b, and theinterdiffusion portion 41 has even more favorable thermal conductivity.As a result, heat that has been generated from the die 10 of thesemiconductor device is even more easily dissipated, and thesemiconductor device is even less likely to be thermally damaged.Crystal orientations of copper crystal structures can be determined froma transmission electronic microscope (TEM) image of the interdiffusionportions 41.

It should be noted that, in order to form a copper crystal structurehaving the same crystal orientation in each interdiffusion portion so asto straddle the bonding interface, it is preferable to use a copperpowder as the copper source for the joint portion. If other coppersources, for example, various types of copper oxides such as cupricoxide are used, even though a sintered body can be obtained, it is noteasy to form a copper crystal structure having the same crystalorientation in each interdiffusion portion so as to straddle the bondinginterface.

In each interdiffusion portion 41, it is sufficient that the crystalorientations at any crystal plane of the copper crystal structure arethe same, and it is not necessary that the crystal orientations are thesame at a specific crystal plane. In an example (FIG. 4), which will bedescribed later, crystal orientations of {111} planes of copper aremeasured; however, the reason for this is that it is easy to observe{111} planes of copper in TEM, and it is not necessary that the {111}planes of copper be in the same direction. Moreover, in the case where asingle copper particle 31 has the crystal structures (crystal grains) ofa plurality of single crystals, the crystal orientation may be differentamong those crystal structures.

From the standpoint of further increasing the efficiency of thermalconduction via the interdiffusion portions 41, each copper crystalstructure having the same crystal orientation preferably has a traverselength (in FIG. 2, width, or length in the plane direction Y, of eachcrystal grain) of not less than 10 nm and more preferably not less than50 nm at the bonding interface 40. The upper limit of the traverselength is not limited, but may typically be about 500 nm. The traverselength can be measured from a transmission electronic microscope (TEM)image of the interdiffusion portions 41. The measurement is performedwith respect to five positions, and the average value is used as thetraverse length.

From the same standpoint as that described above, each copper crystalstructure having the same crystal orientation preferably has a maximumthickness straddling the bonding interface 40 of not less than 10 nm andmore preferably not less than 50 nm. The upper limit of the thickness ofthe crystal structure straddling the bonding interface 40 is notlimited, but may typically be about 1000 nm and more typically about 500nm. The thickness can be measured from a transmission electronicmicroscope (TEM) image of the interdiffusion portions 41. Themeasurement is performed at five positions that are located at regularintervals along the direction of the plane of the bonding interface, andthe largest value is used as the thickness.

In the bonding structure 1 having the above-described structure, sincethe sintered body 32 contains copper, and the support 20 is made ofmetal, electrical continuity is established between the sintered body 32and the support 20. On the other hand, electrical continuity between thesintered body 32 and the die 10 may be established or may not beestablished. Considering that an object of the present invention is todissipate heat generated from the die 10 of the semiconductor device, itis clear that the establishment of electrical continuity between thesintered body 32 and the support 20 and the establishment of electricalcontinuity between the sintered body 32 and the die 10 are not essentialto the present invention.

Although a case in which the joint portion is composed of a sinteredbody made of a copper powder has been described above, the joint portionmay also be composed of a sintered body of nickel powder or a sinteredbody of silver powder, instead of the sintered body of a copper powder.In this case, the material for the outermost surface of the support isnickel when a sintered body of nickel powder is used or is silver when asintered body of silver powder is used. Then, in the bonding structureof the present invention, when the sintered body of nickel powder isused, interdiffusion portions including nickel contained in the supportand nickel contained in the sintered body are formed so as to straddlethe bonding interface between the support and the sintered body. Whenthe sintered body of silver powder is used, interdiffusion portionsincluding the silver of the support and the silver of the sintered bodyare formed so as to straddle the bonding interface between the supportand the sintered body.

In both the case where interdiffusion portions of nickel are formed inthe joint portion and the case where interdiffusion portions of silverare formed in the joint portion, it is preferable that, in each of theinterdiffusion portions, a nickel or silver crystal structure having thesame crystal orientation is formed so as to straddle the bondinginterface, because the joint portion thereby has even more favorablethermal conductivity. In the interdiffusion portions, it is sufficientthat the crystal orientations at any crystal plane of the nickel orsilver crystal structure are the same, and it is not necessary that thecrystal orientations are the same at a specific crystal plane.

With respect to details of the cases where the joint portion is composedof nickel or silver, details of the above-described case where the jointportion is composed of copper will be appropriately applied to thosepoints that are not elaborated.

FIG. 3 shows another embodiment of the die bonding joining structure ofthe present invention. It should be noted that the description of theembodiment shown in FIGS. 1 and 2 will be appropriately applied to thosepoints that are not elaborated regarding the present embodiment. Thepresent embodiment relates to the support 20 having the outermostsurface of a base material 20 a of the support 20 being composed of goldalone 20 b, and the bonding structure 1 that is formed by sintering acopper powder composed of copper alone. In the bonding structure 1, itis preferable that the interdiffusion portions 41 contain Cu₃Au.Preferably, Cu₃Au is in an alloyed state. A portion 41 c that iscomposed of Cu₃Au has favorable thermal conductivity. As a result, heatthat has been generated from the die 10 of the semiconductor device isdissipated even more. Therefore, the semiconductor device is even lesslikely to be thermally damaged.

The presence of the Cu₃Au portion 41 c in the alloyed state in eachinterdiffusion portion 41 can be confirmed by performing element mappingof the interdiffusion portion 41 and determining the elementdistribution along the vertical cross-sectional direction X. In thiselement distribution, if a region in which the molar ratio of copper togold is 3:1 and where the molar ratio is maintained can be identified,it can be judged that Cu₃Au in the alloyed state is present in thatregion. Moreover, the presence or absence of Cu₃Au in the alloyed statecan also be judged by performing electron diffraction measurement of theinterdiffusion portions 41.

It is more preferable that, in addition to including the Cu₃Au portion41 c, each interdiffusion portion 41 of the bonding structure 1 of theembodiment shown in FIG. 3 includes a solid solution portion 41 d thatis composed of a solid solution of gold and copper. The solid solutionportion 41 d is a portion composed of a solid solution of gold in copperwhich serves as the base material. In the solid solution portion 41 d,it is preferable that the distribution of copper when viewed along thevertical cross-sectional direction X of the bonding structure 1gradually decreases from the sintered body 32 side toward the support 20side. On the other hand, with regard to the distribution of gold, it ispreferable that the distribution of gold when viewed along the verticalcross-sectional direction X of the bonding structure 1 graduallyincreases from the sintered body 32 side toward the support 20 side.Preferably, in each interdiffusion portion 41, the solid solutionportion 41 d is located between the Cu₃Au portion 41 c and the sinteredbody 32, and due to this arrangement, the solid solution portion 41 dhas the function of increasing the bonding strength between the Cu₃Auportion 41 c and the sintered body 32. Moreover, the solid solutionportion 41 d also has the function of smoothly conducting heat from thesintered body 32 to the Cu₃Au portion 41 c. From the standpoint ofmaking these functions even more prominent, it is preferable that theratio between copper and gold in the solid solution portion 41 d varieswithin a range from 0.01 mol or more to 0.33 mol or less of gold withrespect to 1 mol of copper.

The presence of the solid solution portion 41 d composed of copper andgold in each interdiffusion portion 41 can be confirmed by performingelement mapping with respect to the solid solution portion 41 d anddetermining the element distribution along the vertical cross-sectionaldirection X. Moreover, whether or not copper and gold form a solidsolution can also be judged by performing electron diffractionmeasurement of the solid solution portion 41 d.

With respect to the bonding structure 1 of the present embodiment, thedie 10 of the semiconductor device may also have a surface layer 10 acomposed of gold alone and located on a bottom surface of the die 10,that is, a surface of the die 10 that opposes the support 20, and thebonding structure 1 may be formed by sintering this die 10 and a copperpowder composed of copper alone. In this case, it is preferable thatinterdiffusion portions 44 containing gold of the surface layer 10 a,which is formed on the bottom surface of the die 10, and copper, whichis the constituent element of the sintered body, are formed so as toindividually straddle a bonding interface 43 between the die 10 and thesintered body 32. These interdiffusion portions 44 each preferablycontain a portion 44 c that is composed of Cu₃Au. Details of theinterdiffusion portions 44 are the same as those of the above-describedinterdiffusion portions 41, and their description is not repeated here.

Furthermore, it is more preferable that, in addition to the Cu₃Auportion 44 c, each interdiffusion portion 44 of the bonding structure 1has a solid solution portion 44 d that is composed of a solid solutionof gold and copper. Preferably, the solid solution portion 44 d islocated between the Cu₃Au portion 44 c and the sintered body 32. In thesolid solution portion 44 d, it is preferable that the distribution ofcopper when viewed along the vertical cross-sectional direction X of thebonding structure 1 gradually decreases from the sintered body 32 sidetoward the die 10 side. On the other hand, with regard to thedistribution of gold, it is preferable that the distribution of goldwhen viewed along the vertical cross-sectional direction X of thebonding structure 1 gradually increases from the sintered body 32 sidetoward the die 10 side.

Since the interdiffusion portions 44 containing Cu₃Au are formed betweenthe die 10 and the sintered body 32, and the interdiffusion portions 44each contain the solid solution portion 44 d in addition to the Cu₃Auportion 44 c, heat that has been generated from the die 10 is smoothlyconducted to the sintered body 32, and this heat is further conducted tothe support 20 via the interdiffusion portions 41 on the support 20side. As a result, heat that has been generated from the die 10 of thesemiconductor device is dissipated even more. Accordingly, thesemiconductor device is even less likely to be thermally damaged.

Next, a preferred method for manufacturing the above-described bondingstructure 1 will be described. First, a case will be described in whichthe bonding structure 1 shown in FIG. 1 is manufactured using a copperpowder whose copper particles are composed of copper alone and a supportwhose outermost surface is composed of copper alone.

Generally, it is preferable that the copper powder is provided in pasteform in view of ease of handling. It is preferable that the pastecontains an organic solvent in addition to the copper powder. The sameorganic solvents as organic solvents that are used in copper conductivepastes can be used as the organic solvent without limitation. Examplesof such organic solvents include monoalcohols, polyalcohols,polyalcohols alkyl ethers, polyalcohol aryl ethers, esters,nitrogen-containing heterocyclic compounds, amides, amines, saturatedhydrocarbons, and the like. These organic solvents can be used alone orin combination of two or more. The concentration of copper in the pasteis appropriately adjusted to a concentration that is suitable forhandling.

The copper powder in paste form is applied to the outermost surface ofthe support 20. For example, the copper powder in paste form can beapplied to the outermost surface of the support 20 using an apparatussuch as a dispenser. At this time, the copper powder in paste form maybe applied in a dotted arrangement like the spots on a dice or may beapplied in a linear arrangement or a planar arrangement. Then, the die10 is placed on the copper powder in paste form. In this state, heatingis performed at a predetermined temperature, and thus, the copperparticles constituting the copper powder are sintered together to givethe sintered body 32. Simultaneously, the copper particles are sinteredwith the outermost surface of the support 20, and the copper particlesare also sintered with the bottom surface of the die 10. Consequently,the die bonding joining structure 1 is formed, and the die 10 is fixedonto the support 20 via the sintered body 32. Moreover, theinterdiffusion portions 41 are formed so as to individually straddle thebonding interface between the support 20 and the sintered body 32.

With respect to the sintering conditions, the sintering temperature ispreferably between 150° C. and 400° C. inclusive and more preferablybetween 230° C. and 300° C. inclusive. On condition that the sinteringtemperature is within this range, the sintering time is preferablybetween 5 minutes and 60 minutes inclusive and more preferably between 7minutes and 30 minutes inclusive. With regard to the sinteringatmosphere, an oxidizing atmosphere such as air, an inert atmospheresuch as nitrogen or argon, or a reducing atmosphere such asnitrogen-hydrogen can be used. Moreover, sintering may be performed in avacuum. In particular, it is preferable to perform sintering in an inertatmosphere such as nitrogen in the presence of triethanolamine, becausea copper crystal structure having the same crystal orientation canthereby be successfully formed in each interdiffusion portion so as tostraddle the bonding interface.

In the case where the joint portion of the bonding structure 1 iscomposed of nickel or silver, nickel powder or silver powder can be usedinstead of the above-described copper powder. In particular, with regardto the nickel powder, it is preferable to use a nickel powder that ismanufactured using a so-called polyol method, which is disclosed in, forexample, JP 2009-187672A or the like, because a nickel crystal structurehaving the same crystal orientation can thereby be successfully formedin each interdiffusion portion so as to straddle the bonding interface.On the other hand, with regard to the silver powder, it is preferable touse a silver powder that is manufactured using a so-called wet reductionmethod, which is disclosed in, for example, JP 2009-242913A or the like,because a silver crystal structure having the same crystal orientationcan thereby be successfully formed in each interdiffusion portion so asto straddle the bonding interface.

In the case where the copper powder is replaced with nickel powder,primary particles of the nickel powder preferably have an averageparticle diameter D between 20 nm and 300 nm inclusive. In the casewhere the copper powder is replaced with silver powder, primaryparticles of the silver powder preferably have an average particlediameter between 0.1 μm and 2 μm inclusive.

Next, a case will be described in which the bonding structure 1 shown inFIG. 3 is manufactured using a copper powder whose copper particles arecomposed of copper alone, a support whose outermost surface is composedof gold alone, and a die whose bottom surface is composed of gold alone.

As is the case with the above-described method, it is preferable to usethe copper powder in paste form. The copper powder in paste form isapplied to the outermost surface of the support 20 using an apparatussuch as a dispenser, for example. At this time, as described above, thecopper powder in paste form can be applied to the entire region of anopposing surface of the die that opposes the support or a portion ofthat opposing surface. For example, the copper powder in paste form maybe applied in a dotted arrangement like the spots on a dice, or may beapplied in a linear arrangement or in a planar arrangement. Then, thedie 10 is placed on the copper powder in paste form. In this state,heating is performed at a predetermined temperature, and thus, thecopper particles that constitute the copper powder are sintered togetherto give the sintered body 32. Simultaneously, the copper particles 31form necking with gold contained in outermost surface of the support 20and gold contained in the bottom surface of the die 10, and mainly thecopper diffuses into gold. Then, gold contained in the outermost surfaceof the support 20 and gold contained in the bottom surface of the die 10form metallic bonds that are mainly composed of Cu₃Au, which in turnconstitute the interdiffusion portions 41 and 44. Furthermore, the solidsolution portions 41 d and 44 d made of copper and gold are formed inthe interdiffusion portions 41 and 44. The sintering conditions are thesame as those of the above-described case.

In each of the above-described manufacturing methods, in order tosuccessfully form the interdiffusion portions, it is advantageous to usea specific copper powder (hereinafter, also referred as to copper powderP) as the copper powder. Specifically, the interdiffusion portions canbe successfully formed by using the copper powder P having an averageparticle diameter D of primary particles between 0.15 μm and 0.6 μminclusive, having the value of the ratio of the average particlediameter D of the primary particles to an average particle diameterD_(BET) that is calculated by assuming a spherical particle shape basedon the BET specific surface area, that is, D/D_(BET) between 0.8 and 4.0inclusive, and having no layer for suppressing the agglomeration ofparticles provided on the surfaces of the particles. It is preferable touse the copper powder P alone or together with another copper powder.From the standpoint of suppressing shrinkage during sintering andincreasing the bonding strength, it is preferable to use the copperpowder P together with another copper powder having a larger particlediameter (e.g., having an average particle diameter D of about 1 to 5μm) than the copper powder P. The copper powder may contain a copperpowder having a layer for suppressing the agglomeration of particlesprovided on the surfaces of the particles as long as the significance ofthe present invention is not impaired. In the case where the copperpowder P is used together with another copper powder, the copper powderP can be used in an amount of preferably not less than 50 mass % andmore preferably not less than 55 mass % relative to the copper powder asa whole. The copper powder P will be described below.

When the average particle diameter D of the primary particles of thecopper powder P is set at not more than 0.6 μm, during formation of thesintered body 32 using the copper powder P, the copper powder P islikely to be sintered at a low temperature, and also, a gap is unlikelyto be formed between the particles 31, and the specific resistance ofthe sintered body 32 can be reduced. On the other hand, when the averageparticle diameter D of the primary particles of the copper powder P isset at not less than 0.15 μm, shrinkage of the particles duringsintering of the copper powder can be prevented. From these standpoints,the average particle diameter D of the primary particles is preferably0.15 to 0.6 μm and more preferably 0.15 to 0.4 μm. The “average particlediameter D of primary particles of “copper powder” refers to a volumeaverage particle diameter that is obtained by observing the copperpowder using a scanning electron microscope at a magnification of 10,000times or 30,000 times, measuring the Ferret diameter in the horizontaldirection with respect to 200 particles in the visual field, andcalculating a sphere-equivalent value from the measured values. From thestandpoint of increasing the dispersibility of the copper powder, it ispreferable that the copper particles 31 have a spherical particle shape.

It is preferable that the copper powder P does not have a layer(hereinafter also referred to as “protective layer”) for suppressing theagglomeration of particles on the surfaces of the particles. Theconfiguration in which the copper powder P has an average particlediameter D within the above-described numerical range and does not havea protective layer on the surfaces of the particles significantlycontributes to favorable low-temperature sinterability of the copperpowder P. The protective layer may be formed by treating the surfaces ofthe copper particles with a surface treating agent in a downstreamprocess of the manufacturing of the copper powder in order to, forexample, increase the dispersibility and the like. Examples of such asurface treating agent include various organic compounds such as fattyacids including stearic acid, lauric acid, and oleic acid, as well ascoupling agents containing a semi-metal or a metal such as silicon,titanium, or zirconium. Furthermore, even in the case where no surfacetreating agent is used in the downstream process of the manufacturing ofthe copper powder, a protective layer may be formed by adding adispersant to a reaction mixture containing the copper source during themanufacturing of the copper powder using a wet reduction method.Examples of such a dispersant include phosphates such as sodiumpyrophosphate and organic compounds such as gum arabic.

From the standpoint of improving the low-temperature sinterability ofthe copper powder P of the present invention even more, it is preferablethat the content of the elements that form the protective layer in thecopper powder is minimized Specifically, the total content of carbon,phosphorus, silicon, titanium, and zirconium, which are present in aconventional copper powder as the components of the protective layer, ispreferably not more than 0.10 mass %, more preferably not more than 0.08mass %, and even more preferably not more than 0.06 mass % relative tothe copper powder.

The smaller the above-described total content, the better. However, ifthe total content is as low as about 0.06 mass %, the low-temperaturesinterability of the copper powder P can be sufficiently improved.Moreover, if the carbon content of the copper powder is excessivelyhigh, a gas containing carbon may be generated when the copper powder Pis sintered to form the sintered body 32, and due to this gas, theresulting film may crack or the film may separate from the substrate.When the above-described total content in the copper powder is low,problems that may be caused by the generation of carbon-containing gascan be prevented.

It is preferable that the copper powder P has a low impurity content anda high copper purity. Specifically, the copper content of the copperpowder is preferably not less than 98 mass %, more preferably not lessthan 99 mass %, and even more preferably not less than 99.8 mass %.

Even though the copper powder P does not have a layer for suppressingthe agglomeration of the particles 31 on the surfaces of the particles31, the primary particles of the copper powder P are unlikely toagglomerate. The extent of agglomeration of the primary particles can beevaluated using, as a measure, the value of D/D_(BET), which is theratio between the average particle diameter D_(BET) that is calculatedby assuming a spherical particle shape based on the BET specific surfacearea and the average particle diameter D of the primary particles. Thevalue of D/D_(BET) of the copper powder is between 0.8 and 4.0inclusive. The value of D/D_(BET) is a measure that indicates how broadthe particle diameter distribution of the copper powder is when comparedwith an ideal monodispersed state of a copper powder that has a uniformparticle diameter and that is free from agglomeration, and can be usedto estimate the degree of agglomeration.

Evaluation of the value of D/D_(BET) is essentially based on the premisethat the copper powder particles have little surface porosity and arehomogenous, and also have a continuous distribution (unimodaldistribution). Under this premise, when the value of D/D_(BET) is 1, itcan be construed that the copper powder is in the above-described idealmonodispersed state. On the other hand, when the value of D/D_(BET) isgreater than 1, it can be estimated that the greater the value ofD/D_(BET), the broader the particle diameter distribution of the copperpowder, and accordingly, the less uniform the particle diameter or thehigher the degree of agglomeration. It is rare that the value ofD/D_(BET) is smaller than 1, and such values are mostly observed withcopper powders in a state that does not meet the above-describedpremise. The “state that does not meet the above-described premise”means, for example, a state in which the surfaces of the particles havepores, a state in which the surfaces of the particles are nonuniform, astate in which the particles agglomerate locally, and the like.

From the standpoint of further reducing agglomeration of the primaryparticles of the copper powder P, the value of D/D_(BET) is preferablybetween 0.8 and 4.0 inclusive and more preferably between 0.9 and 1.8inclusive. The value of D_(BET) can be obtained by measuring the BETspecific surface area of the copper powder P using a gas absorptionmethod. The BET specific surface area is measured according to asingle-point method using a FlowSorb 112300 manufactured by ShimadzuCorporation, for example. The amount of powder to be measured is set at1.0 g. With regard to the preliminary degassing conditions, thedegassing is performed at 150° C. for 15 minutes. The average particlediameter D_(BET) is calculated from the obtained value of the BETspecific surface area (SSA) and the density (8.94 g/cm³) of copper atabout room temperature using the equation below:D _(BET)(μm)=6/(SSA(m²/g)×8.94(g/cm³))

The value of D_(BET) itself is preferably between 0.08 μm and 0.6 μminclusive, more preferably between 0.1 μm and 0.4 μm inclusive, and evenmore preferably between 0.2 μm and 0.4 μm inclusive. The value of theBET specific surface area of the copper powder P is preferably between1.7 m²/g and 8.5 m²/g inclusive and more preferably between 2.5 m²/g and4 m²/g inclusive.

The copper powder P has a crystallite diameter of preferably not morethan 60 nm, more preferably not more than 50 nm, and even morepreferably not more than 40 nm. The lower limit value of the crystallitediameter is preferably 20 nm. The low-temperature sinterability of thecopper powder can be improved even more by setting the size of thecrystallite diameter within this range. The crystallite diameter isobtained by performing X-ray diffraction measurement of the copperpowder using a RINT-TTR III manufactured by Rigaku Corporation, forexample, and calculating the crystallite diameter (nm) according to aScherrer method using the obtained {111} peak.

Such the copper powder P has the feature of being easy to sinter even ata low temperature. Use of the copper powder P that is easy to sintereven at a low temperature facilitates the formation of a metallic bondbetween the die or the support and the sintered body during bonding ofthe die and the support via the sintered body of the copper powder, andconsequently makes it possible to easily obtain the interdiffusionportions of the present invention.

Whether or not a copper powder is easy to sinter at a low temperaturecan be judged using the sintering onset temperature of that copperpowder as a measure. The copper powder P that is preferably used in thepresent invention has a sintering onset temperature of preferablybetween 170° C. and 240° C. inclusive, more preferably between 170° C.and 235° C. inclusive, and even more preferably between 170° C. and 230°C. inclusive.

The above-described sintering onset temperature can be measured byallowing the copper powder P to stand in a furnace with a 3 vol % H₂—N₂atmosphere and gradually increasing the temperature in the furnace.Specifically, the sintering onset temperature can be measured using amethod that will be described below. Whether or not sintering hasstarted is judged by observing the copper powder P taken out of thefurnace, under a scanning electron microscope to see if surfaceassociation has occurred between particles. “Surface association” refersto a state in which particles are connected to each other such that thesurface of a particle is continuous with the surface of anotherparticle.

Method for Measuring Sintering Onset Temperature

A copper powder is placed on an aluminum table and kept at a settemperature of 160° C. for 1 hour in a 3 vol % H₂—N₂ atmosphere. Then,the copper powder is taken out of the furnace, and the copper powder isobserved under a scanning electron microscope at a magnification of50,000 times to see if surface association has occurred. In the casewhere surface association is not observed, the set temperature of thefurnace is reset at a temperature that is 10° C. higher than theaforementioned set temperature, and whether or not surface associationhas occurred is examined in the same manner as described above at thenew set temperature. This operation is repeated, and the set temperatureof the furnace at which surface association is observed is used as thesintering onset temperature (° C.).

Next, a preferred method for manufacturing the above-described copperpowder will be described. The present manufacturing method is based onthe wet reduction of copper ions using hydrazine as a reducing agent,and one of the features of this method is that an organic solvent thatis miscible with water and capable of reducing the surface tension ofwater is used as a solvent. Since the present manufacturing method usessuch an organic solvent, the copper powder can be manufactured in aneasy and simple manner.

In the present manufacturing method, a reaction mixture containing waterand the above-described organic solvent as a liquid medium and alsocontaining a monovalent or divalent copper source is mixed withhydrazine, and the copper source is reduced to generate copperparticles. In the present manufacturing method, an operation forintentionally forming a protective layer is not performed.

Examples of the organic solvent include monohydric alcohols, polyhydricalcohols, esters of polyhydric alcohols, ketones, and ethers. Themonohydric alcohols preferably have 1 to 5 carbon atoms and morepreferably 1 to 4 carbon atoms. Specific examples of the monohydricalcohols include methanol, ethanol, n-propanol, isopropanol, andt-butanol.

Examples of the polyhydric alcohols include diols, such as ethyleneglycol, 1,2-propylene glycol, and 1,3-propylene glycol, and triols, suchas glycerol. Examples of the esters of polyhydric alcohols include fattyacid esters of the above-described polyhydric alcohols. For example, thefatty acid is preferably a monovalent fatty acid having 1 to 8 carbonatoms and more preferably 1 to 5 carbon atoms. The esters of polyhydricalcohols preferably have at least one hydroxyl group.

The ketones preferably have 1 to 6 carbon atoms and more preferably 1 to4 carbon atoms in the alkyl group bonded to the carbonyl group. Specificexamples of the ketones include ethyl methyl ketone and acetone.Examples of the ethers include dimethyl ether, ethyl methyl ether, anddiethyl ether; oxetane, tetrahydrofuran, and tetrahydropyran, which arecyclic ethers; and macromolecular compounds such as polyethylene glycoland polypropylene glycol, which are polyethers.

Among the above-described various organic solvents, monohydric alcoholsare preferably used in light of economic efficiency, safety, and thelike.

In the above-described liquid medium, the ratio (mass of organicsolvent/mass of water) of the mass of the organic solvent to the mass ofwater is preferably 1/99 to 90/10 and more preferably 1.5/98.5 to 90/10.When the ratio between water and the organic solvent is within thisrange, the surface tension of water during wet reduction can beappropriately reduced, so that a copper powder with the values of D andD/D_(BET) within the above-described ranges can be easily obtained.

The above-described liquid medium is preferably composed only of theorganic solvent and water. This is preferable from the standpoint of,for example, manufacturing a copper powder with no protective layer andfew impurities without using a dispersant or the like.

In the present manufacturing method, a reaction mixture is prepared bydissolving or dispersing a copper source in the above-described liquidmedium. An example of the method for preparing the reaction mixture is amethod in which the liquid medium and the copper source are mixed andstirred. In the reaction mixture, the proportion of the copper sourcerelative to the liquid medium is set such that the weight of the liquidmedium per 1 g of the copper source is preferably between 4 g and 2000 ginclusive and more preferably between 8 g and 1000 g inclusive. It ispreferable that the proportion of the copper source relative to theliquid medium is within this range, because the productivity of copperpowder synthesis can thereby be increased.

Various monovalent or divalent copper compounds can be used as theabove-described copper source. In particular, it is preferable to usecopper acetate, copper hydroxide, copper sulfate, copper oxide, orcuprous oxide. When these copper compounds are used as the coppersource, a copper powder with the values of D and D/D_(BET) within theabove-described ranges can be easily obtained. Also, a copper powderwith few impurities can be obtained.

Then, the above-described reaction mixture is mixed with hydrazine. Theamount of hydrazine to be added is preferably between 0.5 mol and 50 molinclusive and more preferably between 1 mol and 20 mol inclusive withrespect to 1 mol of copper. When the amount of hydrazine to be added iswithin this range, a copper powder having the value of D/D_(BET) withinthe above-described range is easily obtained. For the same reason, thetemperature of the reaction mixture is preferably maintained at atemperature between 40° C. and 90° C. inclusive and more preferablybetween 50° C. and 80° C. inclusive from the start to the end of themixing. For the same reason, it is preferable to continue stirring thereaction mixture from the start to the end of the mixing.

It is preferable that the reaction mixture and hydrazine are mixed usingeither a method (a) or a method (b) below. In this manner, theoccurrence of a problem due to a rapid reaction can be effectivelyprevented.

(a) Hydrazine is added to the reaction mixture a plurality of times atintervals.

(b) Hydrazine is added to the reaction mixture continuously for apredetermined period of time.

In the case (a), the “plurality of times” is preferably between about 2times and 6 times inclusive. The intervals between additions ofhydrazine are preferably between about 5 minutes and 90 minutesinclusive.

In the case (b), the “predetermined period of time” is preferablybetween about 1 minute and 180 minutes inclusive. It is preferable tocontinue stirring of the reaction mixture even after the completion ofmixing with hydrazine to allow the reaction mixture to age. The reasonfor this is that, in this manner, a copper powder with the value ofD/D_(BET) within the above-described range is easily obtained.

In the present manufacturing method, it is preferable to use onlyhydrazine as the reducing agent, because a copper powder with fewimpurities can thereby be obtained. In this manner, a target copperpowder can be obtained.

Although the present invention has been described based on the preferredembodiments above, the present invention is not limited to the foregoingembodiments. For example, in the embodiment shown in FIG. 1, crystalorientations of the copper crystal structures in the interdiffusionportions 41 may be determined with respect to a crystal plane other than{111} planes adopted in examples described later.

Moreover, although the foregoing embodiments are directed to a diebonding structure in which a die of a semiconductor device is used asthe heat generating body, the present invention is not limited to this,and the present invention can be applied to bonding joint that uses amember other than a die of a semiconductor device as the heat generatingbody.

EXAMPLES

Hereinafter, the present invention will be described in greater detailusing examples. However, the scope of the present invention is notlimited to the examples below. It should be noted that, unless otherwisespecified, “%” means “mass %”, and “parts” means “parts by mass”.

Example 1

In the present example, a die bonding joining structure having thestructure shown in FIG. 1 was produced.

(1) Production of Copper Powder and Copper Paste

A 500-ml round-bottomed flask provided with a stirring blade wasprepared. As a copper source, 15.71 g of copper acetate monohydrate wasput into this round-bottomed flask. Furthermore, 10 g of water and 70.65g of isopropanol serving as an organic solvent were put into thisround-bottomed flask to obtain a reaction mixture. This reaction mixturewas heated to 60° C. while being stirred at 150 rpm. While stirring wascontinued, 1.97 g of hydrazine monohydrate was added to the reactionmixture all at once. Then, the reaction mixture was stirred for 30minutes. After that, 17.73 g of hydrazine monohydrate was added to thereaction mixture. The reaction mixture was further stirred for 30minutes. After that, 7.88 g of hydrazine monohydrate was added to thereaction mixture. Then, the reaction mixture was continuously stirredfor 1 hour while the temperature of the reaction mixture was kept at 60°C. After the reaction was completed, the entire amount of the reactionmixture was separated into solid and liquid portions. The obtained solidportion was washed through decantation using pure water. The washing wasrepeated until the conductivity of the supernatant was 1000 μS/cm orless. The washed product was separated into solid and liquid portions.Then, 160 g of ethanol was added to the obtained solid portion, and themixture was filtered using a pressure filter. The filter cake was driedunder reduced pressure at an ordinary temperature to give a targetcopper powder. With respect to this copper powder, the average particlediameter D of primary particles was 0.19 μm, the BET specific surfacearea (SSA) was 3.91 m²/g, D_(BET) was 0.17 μm, D/D_(BET) was 1.1, thetotal content of C, P, Si, Ti, and Zr was 0.05%, the copper content wasmore than 99.8%, the crystallite diameter was 35 nm, and the sinteringonset temperature was 170° C. This copper powder was mixed with a copperpowder composed of copper particles formed through wet synthesis,namely, CS-20 (trade name) (cumulative volume particle diameter D₅₀=3.0μm, which was measured at a cumulative volume of 50 vol % using a laserdiffraction/scattering type particle size distribution measurementmethod) manufactured by Mitsui Mining & Smelting Co., Ltd. in a massratio of 56:44 to obtain a mixed copper powder. This mixed copper powderwas mixed with triethanolamine, 3-glycidoxypropyltrimethoxysilane andmethanol all of which are a mixed organic solvent, to prepare a copperpaste. In the mixed organic solvent, the proportion of triethanolaminewas 54%, the proportion of 3-glycidoxypropyltrimethoxysilane was 29%,and the proportion of methanol was 17%. The proportion of the mixedcopper powder in the copper paste was 86%, and the proportion of theorganic solvent was 14%.

(2) Production of Die Bonding Joining Structure

The copper paste was applied to five positions on a 10-mm-square supportmade of oxygen-free copper (99.96% purity) and having a thickness of 0.5mm through screen printing using a resin film screen with a thickness of50 μm such that the applied copper paste at each position was formedinto a shape with a diameter of 0.8 mm Oxygen-free copper (99.96%purity) formed into a shape that was 5 mm square with a thickness of 1mm was placed on the center of the support as a die. Sintering wasperformed in a nitrogen atmosphere at 260° C. for 10 minutes to give atarget bonding structure. FIGS. 4(a) to 4(c) show TEM images of aportion in the vicinity of a bonding interface between the sintered bodyand the support of the obtained bonding structure. As is clear fromthese images, it can be seen that an interdiffusion portion in whichcopper contained in the support and the copper contained in the sinteredbody are diffused to each other was formed so as to straddle the bondinginterface between the support and the sintered body, and a coppercrystal structure having the same crystal orientation was formed in theinterdiffusion portion so as to straddle the bonding interface. Thecopper crystal structure having the same crystal orientation had atraverse length of 94 nm at the bonding interface. Moreover, the maximumthickness of the copper crystal structure straddling the bondinginterface was 170 nm.

Comparative Example 1

(1) Production of Copper Paste

A mixed copper powder was used in which a copper powder composed ofcopper particles formed through wet synthesis, namely, 1050Y (tradename) manufactured by Mitsui Mining & Smelting Co., Ltd. and a copperpowder composed of copper particles formed through wet synthesis,namely, 1300Y (trade name) manufactured by Mitsui Mining & Smelting Co.,Ltd. were mixed in a mass ratio of 56:44. Both of the two types ofcopper powders that were used in Comparative Examples 1 and 2 had anorganic protective layer on the surfaces of the particles thereof.Otherwise, the procedure was performed in the same manner as in (1) ofExample 1, and thus a copper paste was prepared.

(2) Production of Die Bonding Joining Structure

A bonding structure was formed in the same manner as in (2) ofExample 1. The obtained bonding structure did not have enough mechanicalstrength to maintain the bonding between the die, the sintered body, andthe support, and it was not possible to evaluate the heat dissipationproperties of the obtained bonding structure and to observe TEM imagesof a portion in the vicinity of the bonding interface between thesintered body and the support.

Comparative Example 2

(1) Production of Copper Paste

A mixed copper powder was used in which a copper powder composed ofcopper particles formed through wet synthesis, namely, 1050Y (tradename) manufactured by Mitsui Mining & Smelting Co., Ltd. and a copperpowder composed of copper particles formed through wet synthesis,namely, 1300Y (trade name) manufactured by Mitsui Mining & Smelting Co.,Ltd. were mixed in a mass ratio of 56:44. A mixed resin in whichRE-303SL, which is a bisphenol F type epoxy resin manufactured by NipponKayaku Co., Ltd., RE-306, which is a phenol novolac type epoxy resinmanufactured by Nippon Kayaku Co., Ltd., RE-310S, which is a bisphenol Atype epoxy resin manufactured by Nippon Kayaku Co., Ltd., GAN, which isa liquid type epoxy resin manufactured by Nippon Kayaku Co., Ltd.,KAYAHARD MCD, which is a hardener manufactured by Nippon Kayaku Co.,Ltd., 2-(3,4-epoxycyclohexyl)ethyltrimethylsilane,3-glycidoxypropyltrimethoxysilane, and Amicure MY24, which is a curingaccelerator manufactured by Ajinomoto Fine-Techno Co., Inc., were mixed.The mixed copper powder and the mixed resin were mixed to prepare acopper paste. The mixed resin contained 31% RE-303SL, 15% RE-306, 15%RE-310S, 6% GAN, 28% KAYAHARD MCD, 1%2-(3,4-epoxycyclohexyl)ethyltrimethylsilane, 1%3-glycidoxypropyltrimethoxysilane, and 3% Amicure MY24. The copper pastecontained 89% mixed copper powder and 11% mixed resin.

(2) Production of Die Bonding Joining Structure

A bonding structure was formed in the same manner as in (2) ofExample 1. TEM images of a portion in the vicinity of the bondinginterface between the sintered body and the support of the obtainedbonding structure were captured, but an interdiffusion portion in whicha copper crystal structure having the same crystal orientation wasformed so as to straddle the bonding interface was not observed.

Comparative Example 3

Comparative Example 3 is an example of a bonding structure in which nocopper powder was used.

(1) Preparation of Soldering Paste

A commercially available soldering paste (composition: Sn 63 mass %-Pb37 mass %, manufactured by Hong Kong Welsolo Metal Technology Co.,Limited) was prepared.

(2) Production of Die Bonding Joining Structure

The soldering paste was applied to five positions on a 10-mm-squaresupport made of oxygen-free copper (99.96% purity) and having athickness of 0.5 mm through screen printing using a resin film screenwith a thickness of 50 μm such that the applied soldering paste at eachposition was formed into a shape with a diameter of 0.8 mm Oxygen-freecopper (99.96% purity) formed into a shape that was 5 mm square with athickness of 1 mm was placed on the center of the support as a die.Sintering was performed in a nitrogen atmosphere at 200° C. for 10minutes to give a bonding structure.

Example 2

In the present example, a die bonding joining structure having thestructure shown in FIG. 3 was produced.

(1) Production of Copper Powder and Copper Paste

A copper powder was obtained in the same manner as in Example 1 exceptthat the amount of isopropanol used was 39.24 g, and the amount of waterused was 50 g. With respect to this copper powder, the average particlediameter D was 0.24 μm, the BET specific surface area (SSA) was 3.17m²/g, D_(BET) was 0.21 μm, D/D_(BET) was 1.2, the total content of C, P,Si, Ti, and Zr was 0.04%, the copper content was more than 99.8%, thecrystallite diameter was 35 nm, and the sintering onset temperature was170° C. This copper powder was mixed with a copper powder composed ofcopper particles formed through wet synthesis, namely, CS-20 (tradename) manufactured by Mitsui Mining & Smelting Co., Ltd. in a mass ratioof 56:44 to obtain a mixed copper powder. After that, the procedure wasperformed in the same manner as in Example 1, and thus a copper pastewas prepared.

(2) Production of Die Bonding Joining Structure

A support was used in which a gold plating layer having a thickness of 1μm was formed on the surface of a 10-mm-square base material made ofnickel and having a thickness of 0.5 mm. The copper paste was applied tofive positions on the surface of the gold plating layer of this supportthrough screen printing using a resin film screen with a thickness of 50μm such that the applied copper paste at each position was formed into ashape with a diameter of 0.8 mm A 5-mm-square nickel plate having athickness of 0.5 mm was placed on the center of the support as a die. Agold plating layer having a thickness of 1 μm was formed on a bottomsurface of the die beforehand. Sintering was performed in a nitrogenatmosphere at 260° C. for 10 minutes to give a target bonding structure.The element distribution in a depth direction in the vicinity of thebonding interface between the sintered body and the support of theobtained bonding structure was determined using a scanning transmissionelectron microscope (manufactured by JEOL Ltd.) provided with anenergy-dispersive X-ray analyzer. FIG. 5 shows the results. As is clearfrom FIG. 5, it can be seen that an interdiffusion portion including aportion composed of Cu₃Au and a portion composed of Au and Cu was formedso as to straddle the bonding interface between the support and thesintered body. It was confirmed from the results of electron diffractionthat the interdiffusion portion was constituted by a Cu₃Au alloy and asolid solution portion composed of a solid solution of Au in Cu.Moreover, it can be seen from FIG. 5 that, in the solid solutionportion, the proportion of copper gradually decreased from the sinteredbody side toward the support side, and the proportion of gold graduallyincreased from the sintered body side toward the support side. In thesolid solution portion, the number of moles of Au with respect to 1 molof Cu was within a range of 0.01 mol to 0.33 mol.

Comparative Example 4

(1) Production of Copper Paste

A copper paste was prepared in the same manner as in (1) of ComparativeExample 1.

(2) Production of Die Bonding Joining Structure

A bonding structure was formed in the same manner as in (2) of Example2. The obtained bonding structure did not have enough mechanicalstrength to maintain the bonding between the die, the sintered body, andthe support, and it was not possible to evaluate the heat dissipationproperties of the obtained bonding structure and to determine theelement distribution in the depth direction of a portion in the vicinityof the bonding interface between the sintered body and the support ofthe obtained bonding structure.

Comparative Example 5

(1) Production of Copper Paste

A copper paste was prepared in the same manner as in (1) of ComparativeExample 2.

(2) Production of Die Bonding Joining Structure

A bonding structure was formed in the same manner as in (2) of Example2. The element distribution in the depth direction in the vicinity ofthe bonding interface between the sintered body and the support of theobtained bonding structure was determined using a scanning transmissionelectron microscope (manufactured by JEOL Ltd.) provided with anenergy-dispersive X-ray analyzer, but an interdiffusion portionincluding a portion composed of Cu₃Au and straddling the bondinginterface between the support and the sintered body was not observed.

Comparative Example 6

(1) Preparation of Soldering Paste

A soldering paste in which no copper powder was used was prepared in thesame manner as in (1) of Comparative Example 3.

(2) Production of Die Bonding Joining Structure

A support was used in which a gold plating layer with a thickness of 1μm was formed on the surface of a 10-mm-square base material made ofnickel and having a thickness of 0.5 mm. The soldering paste was appliedto five positions on the surface of the gold plating layer of thissupport through screen printing using a resin film screen having athickness of 50 μm such that the applied soldering paste at eachposition was formed into a shape with a diameter of 0.8 mm A 5-mm-squarenickel plate having a thickness of 0.5 mm was placed on the center ofthe support as a die. A gold plating layer having a thickness of 1 μmwas formed on a bottom surface of the die beforehand. Sintering wasperformed in a nitrogen atmosphere at 200° C. for 10 minutes to give abonding structure.

Evaluation

The heat dissipation properties of the die bonding joining structuresobtained in the examples and the comparative examples were evaluatedusing a method described below. Table 1 below shows the results withrespect to the above-described example and comparative examplesregarding the die bonding joining structures with the structure shown inFIG. 1. Table 2 below shows the results with respect to theabove-described example and comparative examples regarding the diebonding joining structures with the structure shown in FIG. 3.

Method for Evaluating Heat Dissipation Properties

Blackening treatment of a back surface, that is, a surface on which thedie was not placed, of the support of each bonding structure wasperformed by applying a carbon spray to that surface. Then, this surfacewas irradiated with a pulsed laser beam at 3 kV using a thermal constantmeasurement apparatus TC-7000 manufactured by Shinku-Riko Inc., and achange in the surface temperature of the die over time after irradiationwas measured using a thermocouple. The time t_((1/2)) taken for thistemperature to rise by ½ of a temperature rise amount ΔT was calculatedfrom the measurement results and used as an index for evaluation of theheat dissipation properties. Here, although the heat dissipationproperties with respect to heat dissipation from the support toward thedie via the joint portion were evaluated for convenience of the test,the direction in which heat is applied is not essential to theevaluation of the present invention. The temperature rise amount ΔTcorresponds to the difference between the maximum temperature valueafter the laser irradiation and the temperature prior to the laserirradiation. A smaller t_((1/2)) indicates faster transfer of the heatincident on the back surface of the support to the surface of the dieand therefore indicates more favorable heat dissipation properties.

TABLE 1 t_((1/2)) [sec] Example 1 0.44 Comparative Example 1 Notmeasurable Comparative Example 2 0.70 Comparative Example 3 0.80

TABLE 2 t_((1/2)) [sec] Example 2 0.52 Comparative Example 4 Notmeasurable Comparative Example 5 0.63 Comparative Example 6 0.60

As is clear from the results shown in Tables 1 and 2, the bondingstructures obtained in the examples had superior heat dissipationproperties to the bonding structures of the comparative examples.

Example 3

In the present example, a die bonding joining structure composed ofnickel and having the structure shown in FIG. 1 was produced.

(1) Production of Nickel Paste

A nickel powder NN-20 manufactured by Mitsui Mining & Smelting Co., Ltd.was used. The average particle diameter D of primary particles of thisnickel powder was 20 nm. A nickel paste was obtained by kneading 85parts of this nickel powder and 15 parts of triethanolamine(manufactured by Kanto Chemical Co., Inc.) using a triple roll mill.

(2) Production of Die Bonding Joining Structure

The nickel paste was applied to a support formed of a 15-mm-squarenickel plate (99.98% purity) with a thickness of 0.1 mm through screenprinting using a metal mask with a thickness of 50 μm such that theapplied nickel paste was formed into a shape 10 mm square. A10-mm-square nickel plate (99.98% purity) with a thickness of 0.1 mm wasplaced on the center of the support as a die. The temperature wasincreased to 300° C. at a rate of 5° C./min in air and was kept for 30minutes to give a target bonding structure. FIG. 7 shows TEM images of aportion in the vicinity of the bonding interface between the sinteredbody and the support of the obtained bonding structure. As is clear fromFIG. 7, it was found that an interdiffusion portion of the nickel of thesupport and the nickel of the sintered body was formed so as to straddlethe bonding interface between the support and the sintered body, and anickel crystal structure having the same crystal orientation was formedin the interdiffusion portion so as to straddle the bonding interface.

Example 4

In the present example, a die bonding joining structure composed ofsilver and having the structure shown in FIG. 1 was produced.

(1) Production of Silver Paste

A silver powder SPQ-05S manufactured by Kamioka Mining and Smelting Co.,Ltd. was used. This silver powder had a crystallite diameter of 21 nm,an average particle diameter D of 1.05 μm, and a specific surface areaof 1.00 m²/g. A silver paste was obtained by kneading 99 parts of thissilver powder, 1 part of ethyl cellulose (ETHOCEL STD 100 manufacturedby Nisshin & Co., Ltd.), and 17 parts of terpineol (manufactured byNippon Terpene Chemicals, Inc.) using a triple roll mill.

(2) Production of Die Bonding Joining Structure

The silver paste was applied to a support formed of a 15-mm-squaresilver plate (99.98% purity) with a thickness of 0.1 mm through screenprinting using a metal mask with a thickness of 50 μm such that theapplied silver paste was formed into a shape 10 mm square. A10-mm-square silver plate (99.98% purity) with a thickness of 0.1 mm wasplaced on the center of the support as a die. The temperature wasincreased to 300° C. at a rate of 5° C./min in air and was kept for 30minutes to give a target bonding structure. FIG. 8 shows TEM images of aportion in the vicinity of the bonding interface between the sinteredbody and the support of the obtained bonding structure. As is clear fromFIG. 8, it was found that an interdiffusion portion in which silvercontained in the support and silver contained in the sintered body arediffused to each other was formed so as to straddle the bondinginterface between the support and the sintered body, and a silvercrystal structure having the same crystal orientation was formed in theinterdiffusion portion so as to straddle the bonding interface.

INDUSTRIAL APPLICABILITY

According to the bonding joining structure of the present invention,heat generated from various heat generating bodies including a die of asemiconductor device is efficiently conducted to a support. That is tosay, the bonding joining structure of the present invention hasexcellent heat dissipation properties. Therefore, the bonding joiningstructure of the present invention is especially useful as a bondingstructure for a power device that is used in a power conversionapparatus, such as a converter or an inverter, for power control of thatpower conversion apparatus.

REFERENCE SIGNS LIST

-   1 Die bonding joining structure-   10 Die of semiconductor device-   20 Support-   30 Joint portion-   31 Copper particle-   32 Sintered body-   40, 43 Bonding interface-   41, 44 Interdiffusion portion

The invention claimed is:
 1. A bonding joining structure in which a heatgenerating body and a support comprising a metal are joined to eachother via a joint portion composed of a sintered body of copper powder,wherein the support contains copper or gold, the copper or gold beingpresent in at least an outermost surface of the support, and aninterdiffusion portion in which copper or gold contained in the supportand copper contained in the sintered body are diffused to each other isformed so as to straddle a bonding interface between the support and thesintered body.
 2. The bonding joining structure according to claim 1,wherein the bonding joining structure is a die bonding joining structurein which a die of a semiconductor device, the die serving as the heatgenerating body, and the support comprising a metal are joined to eachother via the joint portion composed of the sintered body of the copperpowder, the support contains copper or gold, the copper or gold beingpresent in at least the outermost surface of the support, and theinterdiffusion portion in which copper or gold contained in the supportand copper contained in the sintered body are diffused to each other isformed so as to straddle the bonding interface between the support andthe sintered body.
 3. The bonding joining structure according to claim2, wherein copper is present in the outermost surface of the support,and a copper crystal structure having the same crystal orientation isformed in the interdiffusion portion so as to straddle the bondinginterface.
 4. The bonding joining structure according to claim 3,wherein the copper crystal structure having the same crystal orientationhas a traverse length of 10 nm or more at the bonding interface.
 5. Thebonding joining structure according to claim 3, wherein a gold layer isformed on a bottom surface of the die, the interdiffusion portion inwhich gold contained in the bottom surface of the die and coppercontained in the sintered body are diffused to each other is formed soas to straddle a bonding interface between the die and the sinteredbody, and the interdiffusion portion contains Cu₃Au.
 6. The bondingjoining structure according to claim 5, wherein the interdiffusionportion contains Cu₃Au and a solid solution of gold and copper.
 7. Thebonding joining structure according to claim 4, wherein a gold layer isformed on a bottom surface of the die, the interdiffusion portion inwhich gold contained in the bottom surface of the die and coppercontained in the sintered body are diffused to each other is formed soas to straddle a bonding interface between the die and the sinteredbody, and the interdiffusion portion contains Cu₃Au.
 8. The bondingjoining structure according to claim 7, wherein the interdiffusionportion contains Cu₃Au and a solid solution of gold and copper.
 9. Thebonding joining structure according to claim 2, wherein gold is presentin the outermost surface of the support, and the interdiffusion portioncontains Cu₃Au.
 10. The bonding joining structure according to claim 9,wherein the interdiffusion portion contains Cu₃Au and a solid solutionof gold and copper.
 11. The bonding joining structure according to claim9, wherein a gold layer is formed on a bottom surface of the die, theinterdiffusion portion in which gold contained in the bottom surface ofthe die and copper contained in the sintered body are diffused to eachother is formed so as to straddle a bonding interface between the dieand the sintered body, and the interdiffusion portion contains Cu₃Au.12. The bonding joining structure according to claim 11, wherein theinterdiffusion portion contains Cu₃Au and a solid solution of gold andcopper.
 13. The bonding joining structure according to claim 2, whereina gold layer is formed on a bottom surface of the die, theinterdiffusion portion in which gold contained in the bottom surface ofthe die and copper contained in the sintered body are diffused to eachother is formed so as to straddle a bonding interface between the dieand the sintered body, and the interdiffusion portion contains Cu₃Au.14. The bonding joining structure according to claim 13, wherein theinterdiffusion portion contains Cu₃Au and a solid solution of gold andcopper.
 15. A bonding joining structure in which a heat generating bodyand support comprising a metal are joined to each other via a jointportion composed of a sintered body of nickel powder, wherein thesupport contains nickel, the nickel being present in at least anoutermost surface of the support, and an interdiffusion portion in whichnickel contained in the support and nickel contained in the sinteredbody are diffused to each other is formed so as to straddle a bondinginterface between the support and the sintered body.
 16. A bondingjoining structure in which a heat generating body and a supportcomprising a metal are joined to each other via a joint portion composedof a sintered body of silver powder, wherein the support containssilver, the silver being present in at least an outermost surface of thesupport, and an interdiffusion portion in which silver contained in thesupport and silver contained in the sintered body are diffused to eachother is formed so as to straddle a bonding interface between thesupport and the sintered body.